The present invention relates to a reciprocating piston engine having cylinders adjacent in the crankshaft direction in an engine case, particularly an internal-combustion engine, comprising a reciprocating drive system for reciprocating pistons which, by way of piston rods by means of a hypocycloidal straight-line mechanism, are in a driving connection with reciprocating and guide eccentrics which are rotationally movable on a crankshaft, a guide element of the straight-line mechanism cooperating with guide surfaces arranged on the engine case.
GB-1 060 372 describes an embodiment of a reciprocating piston engine having diametrically arranged cylinder pairs whose parallel axes orthogonally intersect the axis of rotation of the crankshaft. This reciprocating piston engine is an internal-combustion engine combined with a reciprocating piston compressor. This known engine comprises a reciprocating drive system with a hypocycloidal straight-line mechanism which comprises eccentrics combined with a crankshaft and non-rotatably connected with one another. Both piston rods, which connect opposing pistons in diametrical cylinders, are jointly in a driving connection with a tube-type reciprocating eccentric constructed of two parts, in whose two end areas one guide eccentric respectively is arranged which has a guide element guided on the engine case side in a straight line in a slidably movable manner.
Cylinder tubes, which in addition are used for the linear guiding of the reciprocating pistons and are arranged to be guided coaxially to the reciprocating pistons in the engine case and, for the slidably movable guiding are in a driving connection with the tube-type reciprocating eccentric are particularly disadvantageous with respect to this known reciprocating drive system. This arrangement results in a reciprocating piston engine which has a long dimension in the longitudinal direction of the crankshaft and disadvantageously large bearing distances for the crankshaft in the engine case.
Another disadvantage is the high-expenditure and complicated construction of this known reciprocating drive system with the hypocycloidal straight-line mechanism with a three-disk eccentric mounted freely rotatably on a crankshaft reciprocating pin and integrally formed.
DE-PS 271 755 describes an embodiment of an internal-combustion engine with a reciprocating piston with diametrically arranged cylinder pairs whose parallel axes extend in a transverse plane with respect to the axis of rotation of the crankshaft. In the case of a reciprocating drive system with a hypocycloidal straight-line mechanism, this arrangement permits the linking of the parallel piston rods to a single guide ring of a reciprocating eccentric non-rotatably arranged in the center between pinions of Cardan's circle pairs.
Although this known arrangement with the hypocycloidal straight-line mechanism results in a reciprocating piston engine which has a short construction in the longitudinal direction of the crankshaft and has relatively short bearing distances of the crankshaft, the low stability of this reciprocating drive system with its toothing is a disadvantage.
Further, DE-A 25 19 908 describes a hypocycloid reciprocating piston engine which, in the plane of the axis of rotation of the crankshaft, has cylinder pairs arranged in an adjacent manner in the direction of the crankshaft, between whose connecting rods another orthogonally directed cylinder pair is provided as the hypocycloidal straight-line mechanism. This cylinder pair has pistons oscillating in additional cylinders of the reciprocating piston engine which are used as guide elements so that this crosswise arrangement of cylinder pairs results in a disadvantageously large-sized internal-combustion engine.
In another embodiment of the species shown in DE-A 25 19 908, instead of guidance by a cylinder pair, a sliding block cooperates with the guide eccentric provided centrally between the piston rods. The block is guided linearly by straight-line mechanisms, rigidly mounted in the engine housing orthogonally to the piston rods. The disadvantage of this arrangement is that the sliding block tends to jam in every TDC range of each piston and this cannot be completely eliminated even by maintaining large parts tolerances and expensive measures.
An object of the present invention is to provide a kinematically advantageous hypocycloidal straight-line mechanism centrally between parallel piston rods in which such straight-line mechanism together with additional features of the present invention permit a compact design with relatively low weight in a surprisingly simple fashion.
This object has been achieved by providing that, on a guide eccentric arranged between the piston rods for reciprocating pistons of cylinders adjacent in banks, a single guide element is used for the straight-line motion of the two piston rods.
The arrangement according to the present invention reduces to a minimum in an advantageous manner the free reciprocating pin length of the crankshaft for two synchronously provided piston pairs. This minimum is the result of the cylinder spacing plus twice half the piston rod thickness. As a result, the webs of the crankshaft can be arranged closely adjacent to the respective piston rod and can be equipped with compensating masses for the reciprocating pistons and piston rod relative to the axis of rotation of the crankshaft, similar to the advantageous development known from the above-mentioned DE-PS 271 755.
The use of a Watt-type control arm suggested in DE-A 41 08 311 as the guide element of the hypocycloidal straight-line mechanism, with a connecting rod mounted between the piston rods on the single guide eccentric makes it possible in another embodiment to equip the swing arms of the guide eccentric, in at least one of its linking points, with an adjusting eccentric arranged rotatably and fixably relative to the connecting rod and/or to the engine case, as the device for compensating dimensional tolerances. After the mounting of the reciprocating drive system, in the center position of the connecting rod, this adjusting eccentric is rotated first in one direction until a resistance occurs, is then rotated in the opposite direction until the next resistance occurs and is finally fixed by taking the mean amount approximately between both resistance positions. While the connecting rod of the Watt-type control arm is encapsulated in the engine case, the engine-case-side linking points of the swivel arms are advantageously equipped with adjusting eccentrics which thereby become accessible, for example, for an automatic adjustment in a series production of the reciprocating piston engine.
For achieving a simple mounting of the guide eccentric in the one piece connecting rod of the Watt-type control arm used as the guide element, the guide eccentric is formed of parts which can be connected in the axial reciprocating-pin direction. A reciprocating eccentric as well as a compensating mass relative to the axis of the crankshaft reciprocating pin is arranged on each part on the piston rod side for obtaining a simpler construction.
The simple design is advantageously reinforced in another embodiment of the present invention by specially designed reciprocating eccentrics being mounted on the guide eccentrics, each in a releasable nonrotatable connection. The need for a nonrotatable connection of the eccentric with the crankshaft reciprocating pin is thereby eliminated and produces a freely rotatable arrangement of the kinematically functionally connected three-disc eccentric in an axially advantageously shorter configuration.